The present invention relates in a general way to a turboprop unit for an aircraft, comprising in particular, from upstream to downstream with respect to the direction of gas flow, a jet engine having a fan casing and a gas exhaust system, these being coaxial with an engine axis, the said gas exhaust system including two afterbody half-cowlings, called D-ducts, each hinged about an axis, enabling them to move, for the purposes of maintenance operations, from a closed position to an open position.
In the closed position, the said afterbody half-cowlings are also connected to the downstream end of the fan casing via a means for sealing and strain transmission, having complementary male and female profiles, called a “V-blade/V-groove” system, the male profile belonging to the afterbody half-cowlings and the female profile belonging to the fan casing side.
In the known art, the downstream outlet plane of the fan casing is strictly perpendicular to the engine axis, and the hinge axes of the half-cowlings are parallel to each other and inclined at an angle α with respect to the engine axis, this angle not being allowed to exceed 2 to 3 degrees, because above this value it would be difficult for the “V-blade/V-groove” system to engage correctly, owing to a “chisel” effect, and, furthermore, the increased friction caused by such a difficult engagement would lead to premature wear.
However, it would be useful to increase this angle α in order to reduce the amount of projection caused by the fairing of the hinges forming the hinge axes of the afterbody half-cowlings. This is because this projection complicates the aerodynamic design of the area in question.